The Analgesia Nociception Index’s Performance During Remimazolam-Based General Anesthesia: A Prospective Observational Study

<i>Background and Objectives</i>: The Analgesia Nociception Index (ANI), a surrogate marker derived from heart rate variability (HRV) analysis, has been validated for assessing the balance between antinociception and nociception during propofol anesthesia. The ANI continuously monitors this balance, with values above 50 indicating optimal analgesia. By adjusting analgesic administration based on ANI values, anesthesiologists can provide more personalized intraoperative pain control. Remimazolam, a novel benzodiazepine anesthetic lacking intrinsic analgesic properties, exhibits distinct HRV patterns compared to propofol. Considering these differences, the validity of the ANI during remimazolam anesthesia remains uncertain. We evaluated the validity of the ANI by assessing its ability to detect nociceptive stimuli during remimazolam anesthesia. <i>Materials and Methods</i>: In total, 28 patients were administered general anesthesia using remimazolam and remifentanil. We evaluated changes in the ANI before and after tetanic stimulation. In addition, we investigated the association between hemodynamic responses during surgical incisions and changes in the ANI. <i>Results</i>: Tetanic stimulation resulted in a significant (<i>p</i> < 0.001) reduction in the ANI, from 62.0 (interquartile range [IQR] 50.5-76.0) to 44.0 (IQR 37.0-55.5). Of the 13 patients who experienced hemodynamic responses during surgical incision, the ANI significantly decreased from 63.2 ± 13.6 to 36.9 ± 13.8 following noxious surgical stimulation (<i>p</i> < 0.001). <i>Conclusions</i>: The ANI reflects the dynamic equilibrium between antinociception and nociception during remimazolam-based general anesthesia.